1. Field of the Invention
The present invention relates generally to a brake booster for an automotive vehicle and more particularly to a control valve for controlling the pressure difference between opposite sides of a power piston in the brake booster in response to brake pedal depressing force.
2. Description of the Prior Art
In conventional brake booster control valves, an example of which is disclosed in U.S. Pat. No. 3,688,647, a poppet member made of resilient material such as rubber is biased forward by a coil spring interposed between the poppet member and a push rod the rear end of which is pivotally connected to a brake pedal. A front end of the push rod is pivotally connected to a plunger member which includes an annular valve seat on a rear end thereof for sealing abutment with the poppet member.
The valve seat of the plunger member of such conventional control valves is normally biased into sealing abutment with the poppet member under non-braking conditions. This can result in the formation of a permanent annular depression in the poppet member in the shape of the sealing surface of the annular valve seat and can require proper radial orientation of the poppet member to effect an adequate seal.
Because the push rod can become slanted during the operation of the brake booster as a result of the mechanical linkage with the foot pedal, as is well known, the coil spring can exert a radial force on the poppet member, causing radial movement of the poppet member relative to the valve seat. This condition can cause the annular valve seat to contact the poppet valve eccentrically to the permanent depression, and can thereby lead to sealing failure between the poppet member and the valve seat of the plunger.